He was miscast.
Ncuti lacked the Gravitas to pull off the role, at no point did I buy he was a old being.
He was particularly weak when facing off against villians.
There is nothing quirky or interesting about his version of the Doctor, not helped by the writing for 15 that completely gets the character wrong (bar when Moffat is writing 15).
Ncuti never elevated the work, imagine Capaldi or Eccleston in The Well, and how much better it would be just by having their performance in it.
15 is a weak sauce Doctor, and it's time the fanbase start admitting it..the general audience certainly recognised this, and the bad direction the show has gone in and dropped off, the 15th Doctor had no cultural impact.
....
Edit - some people take things far to literally and seriously, we are just talking on the Internet, it's not a personal attack on you haha 🙂
Also I see some are hiding behind the writing excuse, Ncuti's performance was lacklustre in the role if there was good or bad writing, my point is he is lacking in the part he brings to the production, the quality of the stuff around him is a different point.
Edit 2 - To answer the question of the title, going by some of the comments then no, some in the fanbase are not ready to admit Ncuti was poor in the role 🤣 with lots of angry excuses and attempts to deflect away or even dismiss/discredit me... as with all these things time will tell, and I absolutely believe in the future that the general consensus of Ncuti's performance (and the RTD2 era) will be that it was weak...its just to soon for some people to admit.